Refrigeration system with brushless dc motor compressor drive

ABSTRACT

A refrigeration system for a temperature-controlled storage device includes a refrigeration circuit, a cooling circuit, and a controller. The refrigeration circuit includes a compressor driven by a brushless DC motor operable at multiple different speeds, a first heat exchanger, an expansion device, and a cooling unit in fluid communication via a first working fluid. The cooling circuit includes a pump and a second heat exchanger in fluid communication with the first heat exchanger via a second working fluid such that the first heat exchanger is liquid-cooled by the second working fluid. The controller operates the brushless DC motor at multiple different speeds to accommodate multiple different thermal loads experienced by the refrigeration system. Each of the speeds corresponds to a different thermal load. The controller modulates the speed of the brushless DC motor to maintain a desired temperature of a temperature-controlled space within the temperature-controlled device.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of and priority as a continuation ofU.S. patent application Ser. No. 14/996,062, filed Jan. 14, 2016, whichclaims priority to U.S. Provisional Patent Application No. 62/104,512,filed Jan. 16, 2015, which are hereby incorporated by reference hereinin their entireties.

BACKGROUND

The present invention relates generally to the field oftemperature-controlled display devices (e.g., refrigerated displaydevices or cases, etc.) having a temperature-controlled space forstoring and displaying products such as refrigerated foods or otherperishable objects. More specifically, the present invention relates torefrigeration system for a temperature-controlled display device. Morespecifically still, the present invention relates to a refrigerationsystem for a temperature-controlled display device that uses a brushlessDC motor to circulate a refrigerant within a refrigeration circuit.

Temperature-controlled display devices (e.g., refrigerators, freezers,refrigerated merchandisers, refrigerated display cases, etc.) may beused in commercial, institutional, and residential applications forstoring or displaying refrigerated or frozen objects. Refrigerateddisplay cases are a type of temperature-controlled storage device thatare often used to display fresh food products (e.g., beef, pork,poultry, fish, etc.) in a supermarket or other commercial setting.Refrigerated display cases typically include cooling elements (e.g.,cooling coils, heat exchangers, evaporators, etc.) that receive acoolant (e.g., a liquid such as a glycol-water mixture, a refrigerant,etc.) from a refrigeration system to provide cooling to thetemperature-controlled space. Fans are typically used to move air overthe cooling elements to facilitate heat transfer thereto. Somerefrigerated display cases have doors that can be opened (e.g., by acustomer) to access products within the temperature-controlled space.Other refrigerated display cases have an open front and use fans tocreate an air barrier (e.g., an air curtain) to prevent outside air fromentering the temperature-controlled space.

Some commercial refrigeration systems (e.g., in a supermarket) usecentralized parallel compressor systems with long liquid and suctionbranches piped to and from the evaporators in the refrigerated displaycases. However, remotely locating elements of the refrigeration system(e.g., compressors, condensers) can result in expensive field piping,large refrigerant charge and leakage, and parasitic heating of theliquid and suction piping. Other commercial refrigeration systems useself-contained refrigerated display cases that include all of thecomponents of the refrigeration system (e.g., contained within a housingof the display case, positioned on top of the display case, etc.).

The compressors used in conventional refrigeration systems often sufferfrom a variety of disadvantages such as a lack of variable capacity,energy inefficiency, excess noise, etc. It would be desirable to providea refrigerated display case with an improved compressor that overcomesthese and other disadvantages.

SUMMARY

One exemplary embodiment relates to a refrigeration system for atemperature-controlled storage device. The refrigeration system includesa refrigeration circuit, a cooling circuit, and a controller. Therefrigeration circuit includes a compressor driven by a brushless DCmotor operable at multiple different speeds, a first heat exchanger, anexpansion device, and a cooling unit in fluid communication via a firstworking fluid. The cooling circuit includes a pump and a second heatexchanger in fluid communication with the first heat exchanger via asecond working fluid such that the first heat exchanger is liquid-cooledby the second working fluid. The controller operates the brushless DCmotor at multiple different speeds to accommodate multiple differentthermal loads experienced by the refrigeration system. Each of thespeeds corresponds to a different thermal load. The controller modulatesthe speed of the brushless DC motor to maintain a desired temperature ofa temperature-controlled space within the temperature-controlled device.

In some embodiments, the refrigeration circuit further includes a firstfan that provides an airflow across the cooling unit to cool theairflow. The cooled airflow may be provided to thetemperature-controlled space within the temperature-controlled device.In some embodiments, the controller modulates a speed of the first fanto modulate a rate of heat transfer experienced by thetemperature-controlled space to maintain the desired temperature of thetemperature-controlled space.

In some embodiments, the controller operates the expansion device tocontrol a flow rate of the first working fluid passing therethrough andentering the cooling unit to modulate a rate of heat transferexperienced by the airflow flowing across the cooling unit to maintainthe desired temperature of the temperature-controlled space.

In some embodiments, the controller modulates the speed of the brushlessDC motor to control a flow rate of the first working circulating throughthe refrigeration circuit to modulate a rate of heat transferexperienced by the airflow flowing across the cooling unit to maintainthe desired temperature of the temperature-controlled space.

In some embodiments, the cooling circuit further includes a second fanthat provides an airflow across the second heat exchanger to cool thesecond working fluid. In some embodiments, the controller modulates aspeed of the second fan to modulate a rate of heat transfer experiencedby the second working fluid flowing through the second heat exchanger.The second working fluid may absorb heat from the first working fluid inthe first heat exchanger to maintain the desired temperature of thetemperature-controlled space.

In some embodiments, the controller modulates a speed of the pump tocontrol a flow rate of the second working fluid circulating through thecooling circuit to modulate a rate of heat transfer from the firstworking fluid to the second working fluid in the first heat exchanger tomaintain the desired temperature of the temperature-controlled space.

In some embodiments, the expansion device is an expansion valveconfigured to adjust expansion of the first working fluid passingtherethrough. In some embodiments, the brushless DC motor isliquid-cooled.

Another exemplary embodiment relates to a refrigeration circuit for atemperature-controlled storage device. The refrigeration circuitincludes a compressor, a variable-speed brushless DC motor, a heatexchanger, an expansion device, a cooling unit, and a controller. Thecompressor circulates a working fluid through the refrigeration circuitand is driven by the variable-speed brushless DC motor. The heatexchanger receives the working fluid from the compressor and providescooling for the working fluid. The expansion device receives the cooledworking fluid from the heat exchanger and expands the working fluid to alower-temperature state. The cooling element receives the expandedworking fluid from the expansion device and provides the working fluidto the compressor. The controller operates the variable-speed brushlessDC motor at multiple different speeds to accommodate multiple differentthermal loads. Each of the speeds corresponds to a different thermalload. The controller modulates the speed of the brushless DC motor tomaintain a desired temperature of a temperature-controlled space withinthe temperature-controlled device. The compressor, the heat exchanger,the expansion device, and the cooling element are in fluid communicationvia the working fluid.

In some embodiments, the refrigeration circuit includes a fan thatprovides an airflow across the cooling element to cool the airflow. Thecooled airflow may be provided to the temperature-controlled spacewithin the temperature-controlled device.

In some embodiments, the controller modulates a speed of the fan tomodulate a rate of heat transfer experienced by thetemperature-controlled space to maintain the desired temperature of thetemperature-controlled space.

In some embodiments, the controller operates the expansion device tocontrol a flow rate of the working fluid passing therethrough andentering the cooling element to modulate a rate of heat transferexperienced by the airflow flowing across the cooling element tomaintain the desired temperature of the temperature-controlled space.

In some embodiments, the controller modulates the speed of the variablespeed brushless DC motor to control a flow rate of the working fluidcirculating through the refrigeration circuit to modulate a rate of heattransfer experienced by the airflow flowing across the cooling elementto maintain the desired temperature of the temperature-controlled space.

In some embodiments, the refrigeration circuit includes a fan thatprovides an airflow across the heat exchanger to cool the working fluidflowing therethrough such that the heat exchanger is air-cooled. Thecontroller may modulate a speed of the fan to modulate a rate of heattransfer experienced by the working fluid flowing through the heatexchanger to maintain the desired temperature of thetemperature-controlled space.

In some embodiments, the refrigeration circuit includes a pressuresensor configured to measure a pressure of the working fluid at an inletof the heat exchanger. The controller may modulate a speed of the fan tocontrol the pressure of the working fluid at the inlet of the heatexchanger.

In some embodiments, the heat exchanger is liquid-cooled with a secondworking fluid. The controller may modulate a flow rate of the secondworking fluid with a valve to modulate a rate of heat transfer betweenthe first working fluid and the second working fluid flowing through theheat exchanger to maintain a desired pressure of the first working fluidat an inlet of the heat exchanger.

In some embodiments, the expansion device is an expansion valveconfigured to adjust expansion of the first working fluid passingtherethrough. In some embodiments, the variable-speed brushless DC motoris liquid-cooled.

Still another exemplary embodiment relates to a refrigeration circuitfor a temperature-controlled storage device. The refrigeration circuitincludes a brushless DC motor operable at multiple different speeds anda controller. The brushless DC motor drives a compressor that circulatesa working fluid through the refrigeration circuit. The controlleroperates the brushless DC motor at multiple different speeds toaccommodate multiple different thermal loads. Each of the speedscorresponds to a different thermal load. The controller modulates thespeed of the brushless DC motor to maintain a desired temperature of atemperature-controlled space within the temperature-controlled device.

In some embodiments, the refrigeration circuit includes a cooling unitand a fan. The cooling unit may be configured to provide cooling for thetemperature-controlled space by transferring heat from thetemperature-controlled space to the working fluid. The fan may providean airflow across the cooling unit to cool the airflow. The cooledairflow may be provided to the temperature-controlled space within thetemperature-controlled storage device.

In some embodiments, the controller modulates a speed of the fan tomodulate a rate of heat transfer experienced by thetemperature-controlled space to maintain the desired temperature of thetemperature-controlled space. In some embodiments, the controllermodulates the speed of the brushless DC motor to control a flow rate ofthe working fluid circulating through the refrigeration circuit.

In some embodiments, the refrigeration circuit includes a heat exchangerand a pressure sensor. The heat exchanger may be configured to providecooling for the working fluid. The pressure sensor may be configured tomeasure a pressure of the working fluid at an inlet of the heatexchanger. The controller may modulate a speed of the fan to control thepressure of the working fluid at the inlet of the heat exchanger.

In some embodiments, the heat exchanger is liquid-cooled with a secondworking fluid. The controller may modulate a flow rate of the secondworking fluid with a valve to modulate a rate of heat transfer betweenthe working fluid and the second working fluid flowing through the heatexchanger to maintain a desired pressure of the working fluid at aninlet of the heat exchanger.

The invention is capable of other embodiments and of being carried outin various ways. Alternative exemplary embodiments relate to otherfeatures and combinations of features as may be recited herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a temperature-controlled display device,according to an exemplary embodiment.

FIG. 2 is a cross-sectional elevation view of the temperature-controlleddisplay device of FIG. 1, according to an exemplary embodiment.

FIG. 3 is a block diagram of an air-cooled refrigeration system whichmay be used in conjunction with the temperature-controlled displaydevice of FIG. 1, according to an exemplary embodiment.

FIG. 4 is a block diagram of a liquid-cooled refrigeration system whichmay be used in conjunction with the temperature-controlled displaydevice of FIG. 1, according to an exemplary embodiment.

FIG. 5 is a block diagram of a refrigeration system with multipleparallel compressors, heat exchangers, and cooling elements which may beused in conjunction with the temperature-controlled display device ofFIG. 1, according to an exemplary embodiment.

DETAILED DESCRIPTION

Referring generally to the FIGURES, a refrigeration system with abrushless DC motor compressor drive and components thereof are shown,according to various exemplary embodiments. The refrigeration system maybe used in conjunction with a temperature-controlled display device(e.g., a refrigerated merchandiser) or other refrigeration device usedto store and/or display refrigerated or frozen objects in a commercial,institutional, or residential setting. The refrigeration system includesa heat exchanger (e.g., a gas cooler, a condenser), an expansion valve,a cooling unit (e.g., an evaporator), and a compressor. The compressoris driven by a brushless DC motor which may be controlled by anelectronic controller. In some embodiments, brushless DC motors are alsoused to drive other components of the refrigeration system (e.g., pumps,fans, etc.).

Advantageously, using a brushless DC motor to drive the compressorprovides a number of advantages over conventional refrigeration systems.For example, using a brushless DC motor to drive a refrigerationcompressor may significantly reduce the power consumption of therefrigeration system relative to compressors that use traditionalbrushed and/or AC motors. The decreased power consumption results in anincreased compressor efficiency and decreases the total cost ofoperating the refrigeration system. The brushless DC motor also has adecreased susceptibility to wear and an increased reliability relativeto traditional compressor motors. Additionally, the brushless DC motorcan be operated (e.g., by the controller) at various speeds to allow thesame compressor to accommodate varying refrigeration loads in an energyefficient manner. These and other advantages of a refrigeration systemwith a brushless DC motor compressor drive are described in greaterdetail below.

Referring now to FIGS. 1-2, a temperature-controlled display device 10is shown, according to an exemplary embodiment. Temperaturecontrolled-display device 10 may be a refrigerator, a freezer, arefrigerated merchandiser, a refrigerated display case, or other devicecapable of use in a commercial, institutional, or residential settingfor storing and/or displaying refrigerated or frozen objects. Forexample, temperature-controlled display device 10 may be a service typerefrigerated display case for displaying fresh food products (e.g.,beef, pork, poultry, fish, etc.) in a supermarket or other commercialsetting.

Temperature-controlled display device 10 is shown as a refrigerateddisplay case having a top 12, bottom 14, back 16, front 18, and sides20-22 that at least partially define a temperature-controlled space 24within which refrigerated or frozen objects can be stored. In someembodiments, front 18 is at least partially open (as shown in FIGS. 1-2)to facilitate access to the refrigerated or frozen objects stored withintemperature-controlled space 24. In other embodiments, front 18 mayinclude one or more doors (e.g., hinged doors, sliding doors, etc.) thatmove between an open position and a closed position. The doors may beinsulated glass doors including one or more transparent panels such thatthe objects within temperature-controlled space 24 can be viewed throughthe doors (i.e., from the exterior of display device 10) when the doorsare closed. Similarly, sides 20-22 may be at least partially open (asshown in FIGS. 1-2) or closed to define side walls oftemperature-controlled space 24.

Temperature-controlled display device 10 is shown to include a pluralityof shelves 26-27 upon which refrigerated or frozen objects can be placedfor storage and/or display. Shelves 26 may be located at various heightswithin temperature-controlled space 24. Shelf 27 defines a lowerboundary of temperature-controlled space 24 and separatestemperature-controlled space 24 from a lower space 32 within whichvarious components of a refrigeration circuit for temperature-controlleddisplay device 10 may be contained.

Space 32 is shown to include a cooling element 28 and a fan 30. Coolingelement 28 may include a cooling coil, a heat exchanger, an evaporator,or other component configured to provide cooling fortemperature-controlled space 24. Cooling element 28 may be part of arefrigeration circuit (e.g., refrigeration circuit 50, 80, and/or 100,shown in FIGS. 3-5) and may be configured to absorb heat from an airflow34 passing over or through cooling element 28. Fan 30 may include one ormore fans configured to cause airflow 34 through cooling element 28. Insome embodiments, fan 30 causes airflow 34 from cooling element 28 topass through a channel 36 along a rear surface 38 and/or upper surface40 of temperature-controlled space 24. Rear surface 38 and/or uppersurface 40 may include a plurality of outlets distributed along channel36 (e.g., holes in rear surface 38 and/or upper surface 40 into channel30) through which airflow 34 can pass from channel 30 intotemperature-controlled space 24.

Referring particularly to FIG. 2, channel 36 is shown to include anoutlet 42 configured to direct airflow 34 downward from a front end ofchannel 36. The downward airflow from outlet 42 may form an air curtain44 between outlet 42 and inlet 46. Air curtain 44 may help retainchilled air within temperature-controlled space 24 and may prevent theingression of ambient air (e.g., warmer air from outsidetemperature-controlled display device 10) into temperature-controlledspace 24. Air curtain 44 and airflow 34 may be created by operating fan30. Fan 30 may be configured to draw airflow 34 through inlet 46 and maycause airflow 34 to pass through cooling element 28. Airflow 34 ischilled by cooling element 28 and is forced into temperature-controlledspace 24 by operation of fan 30.

Referring now to FIGS. 3-5, several refrigeration systems 50, 80, and100 which may be used in conjunction with temperature-controlled displaydevice 10 are shown, according to an exemplary embodiment. Referringparticularly to FIG. 3, an air-cooled refrigeration system 50 is shown,according to an exemplary embodiment. Refrigeration system 50 is shownto include a refrigeration circuit 52 including an air cooled condenseror cooler, shown as heat exchanger 54, an expansion device, shown asexpansion valve 56, a cooling unit (e.g., evaporator, heat exchanger,etc.), shown as cooling element 28, and a driver, shown as compressor60.

Compressor 60 may be configured to circulate a refrigerant throughrefrigeration circuit 52. Compressor 60 may compress the refrigerant toa high pressure, high temperature state and discharge the compressedrefrigerant into line 66. Compressor 60 may be a reciprocatingcompressor, a scroll compressor, a rotary compressor, or any other typeof compressor that can be used to compress the refrigerant. In someembodiments, compressor 60 is driven by a brushless DC motor.Advantageously, using a brushless DC motor with compressor 60 enablescompressor 60 to operate at variable speeds and/or capacities. In someembodiments, the brushless DC motor and/or compressor 60 are liquid(e.g., water, glycol, etc.) cooled. In other embodiments, the brushlessDC motor and/or compressor 60 are air cooled. In still otherembodiments, at least one of the brushless DC motor and compressor 60are liquid and air cooled. In some embodiments, compressor 60 isoperated by a controller 62. Controller 62 may adjust the speed ofcompressor 60 based on the refrigeration load (e.g., to control a flowrate of the working fluid to modulate a rate of heat transfer to airflow34 to maintain a desired temperature of the temperature-controlled space24, etc.). Since the speed of compressor 60 is adjustable, a singlecompressor 60 can be used for a variety of applications and canaccommodate multiple different refrigeration loads without sacrificingenergy efficiency. Other features and advantages of the brushless DCmotor are described in greater detail below.

Heat exchanger 54 may be configured to cool the compressed refrigerantin line 66. In various embodiments, heat exchanger 54 may be a gascooler (i.e., a heat exchanger configured to remove heat from gaseousrefrigerant without causing condensation) or a condenser (i.e., a heatexchanger configured to condense a gaseous refrigerant to a liquid ormixed gas-liquid state). In refrigeration system 50, heat exchanger 54is an air-cooled heat exchanger which transfers heat from the compressedrefrigerant into an airflow 68 caused by a fan 64. Fan 64 may becontrolled by controller 62 to modulate the rate of heat transfer inheat exchanger 54 (e.g., between the working fluid and the airflow 68,etc.). In some embodiments, fan 64 is a variable speed fan capable ofoperating at multiple different speeds. Controller 62 may increase ordecrease the speed of fan 64 in response to various inputs fromrefrigeration circuit 50 (e.g., temperature measurements, pressuremeasurements, humidity measurements, enthalpy measurements, etc.). Forexample, a pressure sensor 67 may be located at the inlet of heatexchanger 54. Pressure sensor 67 may be configured to measure thepressure of the working fluid in line 66, at the inlet of heat exchanger54. Controller 62 may be configured to modulate the speed of fan 64 tocontrol the pressure of the working fluid at the inlet of heat exchanger54 (i.e., the pressure measured by pressure sensor 67).

Still referring to FIG. 3, line 70 is shown connecting an outlet of heatexchanger 54 to an inlet of expansion valve 56. Expansion valve 56 maybe configured to expand the refrigerant in line 70 to a low temperatureand low pressure state. Expansion valve 56 may be fixed position valvesor variable position valves. Expansion valve 56 may be actuated manuallyor automatically (e.g., by controller 62 via a valve actuator) to adjustthe expansion (or flow rate) of the refrigerant passing therethrough. Insome embodiments, expansion valve 56 may be operated as a fluid controlvalve to direct the refrigerant through cooling element 28. Expansionvalve 56 may output the expanded refrigerant into line 72. Line 72 isshown extending from an outlet of expansion valve 56 to an inlet ofcooling element 28.

Cooling element 28 may be the same as described with reference to FIGS.1-2. For example, cooling element 28 may include cooling coils, heatexchangers, evaporators, or other components configured to providecooling for temperature-controlled space 24. Cooling element 28 may beconfigured to absorb heat from airflow 34 passing over or throughcooling element 28 and transfer the absorbed heat into the refrigerant.Fan 30 may be controlled by controller 62 to modulate the rate of heattransfer from temperature-controlled space 24 into cooling element 28.In some embodiments, fan 30 is a variable speed fan capable of operatingat multiple different speeds. Controller 62 may increase or decrease thespeed of fan 30 in response to various inputs from refrigeration circuit52 (e.g., temperature measurements, humidity measurements, enthalpymeasurements, etc.). Cooling element 28 may output the refrigerant intoline 74, which connects cooling element 28 to the suction side ofcompressor 60.

Referring now to FIG. 4, a liquid-cooled refrigeration system 80 isshown, according to an exemplary embodiment. In some embodiments,liquid-cooled refrigeration system 80 may be used in conjunction withtemperature-controlled display device 10. Liquid-cooled refrigerationsystem 80 is shown to include refrigeration circuit 82 and a separatecooling circuit 84. Refrigeration circuit 82 may include many of thesame components of refrigeration circuit 52, as described with referenceto FIG. 3. For example, refrigeration circuit 82 is shown to includeexpansion valve 56, cooling element 28, and compressor 60, which mayoperate as described with reference to refrigeration circuit 52.However, refrigeration circuit 82 includes a liquid-cooled cooler orcondenser, shown as heat exchanger 94, in place of heat exchanger 54.

Liquid-cooled heat exchanger 94 receives the compressed refrigerant fromline 66. Liquid-cooled heat exchanger 94 also receives a separate heatexchange fluid (e.g., water, glycol, etc.) from cooling circuit 84 andtransfers heat from the compressed refrigerant into the heat exchangefluid in cooling circuit 84. Cooling circuit 84 is shown to include apump 86 which operates to circulate the heat exchange fluid between heatexchanger 94 and another heat exchanger 92. Pump 86 may be controlled bycontroller 62 to modulate a flow rate of the heat exchange fluidthroughout cooling circuit 84 to thereby modulate the rate of heattransfer from the heat exchange fluid into airflow 90 (e.g., within heatexchanger 92, etc.). In some embodiments, controller 62 is configured tooperate a valve 95 of cooling circuit 84 to modulate the flow rate ofthe heat exchange fluid through cooling circuit 84. Controller 82 mayoperate valve 95 to maintain a desired pressure and/or temperature ofthe working fluid in refrigeration circuit 82 at the inlet of heatexchanger 94 (e.g., the pressure measured by pressure sensor 67).

In heat exchanger 92, the heat exchange fluid rejects the absorbed heatto an airflow 90 passing over or through heat exchanger 92. In someembodiments, airflow 90 is created by operation of a fan 88. Fan 88 maybe controlled by controller 62 to modulate the rate of heat transferfrom the heat exchange fluid into airflow 90 (e.g., within heatexchanger 92, etc.). In some embodiments, heat exchanger 92 and/or heatexchanger 94 is a heat-reclaim heat exchanger configured to use the heatabsorbed from the compressed refrigerant for heating purposes (e.g.,heating water, providing heat to a space, melting frost or ice,anti-condensate heating for display device 10, etc.).

In some embodiments, compressor 60 and/or the DC brushless motor ofcompressor 60 are liquid cooled by the cooling circuit 84 (e.g., via theseparate heat exchange fluid, etc.). For example, the heat exchangefluid that circulates within cooling circuit 84 may be used to providedirect liquid cooling for compressor 60 and/or the brushless DC motorthat drives compressor 60. In some embodiments, the heat exchange fluidfrom cooling circuit 84 is routed to compressor 60 before or afterpassing through heat exchanger 94 such that the heat exchange fluidabsorbs heat from both heat exchanger 94 and compressor 60 in series. Inother embodiments, the heat exchange fluid from cooling circuit 84 maybe routed to compressor 60 in parallel with heat exchanger 94 such thata first portion of the heat exchange fluid absorbs heat from heatexchanger 94 and a second portion of the heat exchange fluid absorbsheat from compressor 60 and/or the brushless DC motor that drivescompressor 60.

In some embodiments, compressor 60 and/or the brushless DC motor areliquid cooled by a second cooling circuit separate from cooling circuit84. The second cooling circuit may be the same or similar to coolingcircuit 84, with the exception that the second cooling circuit absorbsheat from compressor 60 and/or the brushless DC motor rather than fromheat exchanger 94. In other embodiments, compressor 60 and/or thebrushless DC motor are air cooled. For example, a fan (e.g., similar tofans 30 and 88) may be included in refrigeration circuit 80 and used toforce an airflow across compressor 60 and/or the brushless DC motor. Theairflow may absorb heat from compressor 60 and/or the brushless DC motorto provide cooling for such components.

Referring now to FIG. 5, another refrigeration system 100 which may beused in conjunction with temperature-controlled display device 10 isshown, according to an exemplary embodiment. Refrigeration system 100 isshown to include a refrigeration circuit 102 which includes multipleinstances of many of the same components of refrigeration circuit 52, asdescribed with reference to FIG. 3. For example, refrigeration system100 is shown to include multiple heat exchangers 54, multiple expansionvalves 56, multiple cooling elements 28, multiple compressors 60, andmultiple fans 30 and 64.

Compressors 60 may be arranged in parallel and may be configured tocirculate a refrigerant through refrigeration circuit 102. In someembodiments, compressors 60 are operated by controller 62. Compressors60 may compress the refrigerant to a high pressure, high temperaturestate and discharge the compressed refrigerant into line 66. In someembodiments, each of compressors 60 is driven by a brushless DC motor,as described with reference to FIG. 3. Advantageously, using a brushlessDC motor to drive compressors 60 allows compressors 60 to operate atvarious speeds to accommodate different refrigeration loads.

Heat exchangers 54 may be arranged in parallel and may be configured tocool the compressed refrigerant in line 66. In various embodiments, heatexchangers 54 may be gas coolers (i.e., heat exchangers configured toremove heat from gaseous refrigerant without causing condensation) orcondensers (i.e., heat exchangers configured to condense a gaseousrefrigerant to a liquid or mixed gas-liquid state). In some embodiments,heat exchangers 54 are air-cooled heat exchangers (as shown in FIG. 5)which transfer heat from the compressed refrigerant to an airflow 68caused by fans 64. In other embodiments, heat exchangers 54 areliquid-cooled heat exchangers (as shown in FIG. 4) and/or heat-reclaimheat exchangers configured to use the heat absorbed from the compressedrefrigerant for heating purposes (e.g., heating water, providing heat toa space, melting frost or ice, anti-condensate heating for displaydevice 10, etc.). Heat exchangers 54 may be configured to transfer heatfrom the compressed refrigerant into another fluid circulating throughheat exchangers 54 (e.g., another refrigerant, a separate refrigerationcircuit, etc.) or into the ambient environment. In some embodiments,refrigeration circuit 102 includes fluid control valves immediatelyupstream or downstream of heat exchangers 54 to direct the refrigerantthrough a subset of heat exchangers 54.

Expansion valves 56 may be arranged in parallel and may be configured toexpand the refrigerant in line 70 to a low temperature and low pressurestate. Expansion valves 56 may be fixed position valves or variableposition valves. Expansion valves 56 may be actuated manually orautomatically (e.g., by controller 62 via a valve actuator) to adjustthe expansion of the refrigerant passing therethrough. In someembodiments, expansion valves 56 may be operated as fluid control valvesto direct the refrigerant through a subset of cooling elements 28. Eachof expansion valves 56 may be positioned upstream of a correspondingcooling element 28. Cooling elements 28 function to absorb heat fromairflow 34 passing over or through cooling elements 28 and intotemperature-controlled space 24. Cooling elements 28 output therefrigerant into line 74, which connects to the suction side ofcompressors 60.

Referring again to FIGS. 3-5, each of refrigeration systems 50, 80, and100 is shown to include a controller 62. Controller 62 may be configuredto operate various components of refrigeration systems 50, 80, and 100to provide refrigeration for temperature-controlled space 24. Forexample, controller 62 may operate compressors 60, fans 30, 64, and 88,expansion valves 56, pump 86, and/or other operable components ofrefrigeration circuits 50, 80 and 100 (e.g., flow control valves,pressure regulation valves, etc.). Controller 62 may also control othercomponents of temperature-controlled display device 10 such as ananti-condensate heaters, a lighting element, a condensate dissipationsystem, and/or other auxiliary components of temperature-controlleddisplay device 10.

Controller 62 may receive input from various sensory devices ofrefrigeration systems 50, 80, and 100 (e.g., temperature sensors,humidity sensors, pressure sensors, enthalpy sensors, voltage sensors,proximity sensors, etc.) Sensors may be disposed at any locationrelative to temperature-controlled display device 10. For example,sensors may be positioned along any of lines 66-74, withintemperature-controlled space 24, within cooling circuit 84, or otherwisepositioned to measure any variable state or condition oftemperature-controlled display device 10. Controller 62 may use thesensory inputs to determine appropriate control outputs for the operablecomponents of refrigeration systems 50, 80, and 100.

In some embodiments, controller 62 receives input from the sensorydevices via a communications interface. The communications interface mayinclude wired or wireless interfaces (e.g., jacks, antennas,transmitters, receivers, transceivers, wire terminals, etc.) forconducting data communications with various systems, devices, ornetworks. For example, the communications interface may include anEthernet card and port for sending and receiving data via anEthernet-based communications network. In another example, thecommunications interface may include a WiFi transceiver forcommunicating via a wireless communications network. The communicationsinterface may be configured to communicate via local area networks orwide area networks (e.g., the Internet, a building WAN, etc.) and mayuse a variety of communications protocols (e.g., TCP/IP, point-to-point,etc.).

In some embodiments, controller 62 uses the communications interface tosend control signals to various operable components of refrigerationsystems 50, 80, and 100. For example, controller 62 may send controlsignals to compressors 60, fans 30, 64, and 88, valves 56, pump 86,and/or other operable components of refrigeration systems 50, 80, and100 (e.g., flow control valves, pressure regulation valves, etc.). Insome embodiments, controller 62 uses the communications interface tocommunicate with other components of temperature-controlled displaydevice 10 such as an anti-condensate heaters, a lighting element, acondensate dissipation system, and/or other auxiliary components.

In some embodiments, controller 62 includes a processing circuit havinga processor and memory. The processor may be a general purpose orspecific purpose processor, an application specific integrated circuit(ASIC), one or more field programmable gate arrays (FPGAs), a group ofprocessing components, or other suitable processing components. Theprocessor may be configured to execute computer code or instructionsstored in memory or received from other computer readable media (e.g.,CDROM, network storage, a remote server, etc.). Memory may include oneor more devices (e.g., memory units, memory devices, storage devices,etc.) for storing data and/or computer code for completing and/orfacilitating the various processes described in the present disclosure.Memory may include random access memory (RAM), read-only memory (ROM),hard drive storage, temporary storage, non-volatile memory, flashmemory, optical memory, or any other suitable memory for storingsoftware objects and/or computer instructions. Memory may includedatabase components, object code components, script components, or anyother type of information structure for supporting the variousactivities and information structures described in the presentdisclosure. Memory may be communicably connected to the processor viathe processing circuit and may include computer code for executing oneor more processes described herein.

In some embodiments, temperature-controlled display device 10 is aself-contained refrigeration unit which includes all of the componentsof the refrigeration system. Various components of refrigeration systems50, 80, and 100 may be located within temperature-controlled displaydevice 10 or proximate to temperature-controlled display device 10. Forexample, cooling elements 28 and expansion valves 56 may be locatedwithin space 32 and/or temperature-controlled space 24 as shown in FIGS.1-2. Compressors 60, heat exchangers 54 and 92-94, fans 30, 64, and 88,pump 86, and/or controller 62 may be located on top oftemperature-controlled display device 10 (i.e., above top 12), behindtemperature-controlled display device 10 (e.g., behind back 14) or in aseparate space within temperature-controlled display device 10 (e.g.,below bottom 14, adjacent to temperature-controlled space 24, etc.).Refrigerant lines 66 and 70-74 may extend within temperature-controlleddisplay device 10 or along a surface of temperature-controlled displaydevice to connect various components of refrigeration systems 50, 80,and 100.

In other embodiments, temperature-controlled display device 10 is partof a distributed refrigeration system. In a distributed refrigerationsystem, cooling elements 28 are located within temperature-controlledspace 24, whereas other components of refrigeration systems 50, 80, and100 may be remotely located. Refrigerant lines 66 and 70-74 may extendbetween temperature-controlled display device 10 and the remote locationto connect various components of refrigeration systems 50, 80, and 100.

In some embodiments, the refrigeration system used bytemperature-controlled display device 10 includes a compressor (e.g.,compressor 60) that is driven by a brushless DC motor. Brushless DCmotors (BLDC motors, BL motors) also known as electronically commutatedmotors (ECMs, EC motors) are synchronous motors that are powered by a DCelectric source via an integrated inverter/switching power supply. Theintegrated inverted/switching power supply produces an AC electricsignal to drive the motor. In this context, AC (alternating current)does not imply a sinusoidal waveform, but rather a bi-directionalcurrent with no restriction on waveform. Additional sensors andelectronics control the inverter output amplitude and waveform (andtherefore percent of DC bus usage/efficiency) and frequency (i.e. rotorspeed). The rotor of a brushless motor is often a permanent magnetsynchronous motor, but can also be a switched reluctance motor orinduction motor. In some embodiments, the coils of the brushless DCmotor are stationary.

Brushless DC motors provide a number of advantages over traditionalbrushed DC motors. For example, brushed DC motors develop a maximumtorque when stationary, linearly decreasing as velocity increases.Brushless DC motors are often higher efficiency and have a lowersusceptibility to mechanical wear. A brushless motor has permanentmagnets which rotate around a fixed armature, eliminating problemsassociated with connecting current to the moving armature. An electroniccontroller (e.g., controller 62) replaces the brush/commutator assemblyof the brushed DC motor, which continually switches the phase to thewindings to keep the motor turning. Controller 62 may perform similartimed power distribution by using a solid-state circuit rather than thebrush/commutator system.

Brushless motors can provide more torque per weight, more torque perwatt (increased efficiency), increased reliability, reduced noise,longer lifetime (no brush and commutator erosion), elimination ofionizing sparks from the commutator, and overall reduction ofelectromagnetic interference (EMI) relative to a brushed motor. With nowindings on the rotor, brushless motors are not subjected to centrifugalforces. Since the windings are supported by the housing, brushlessmotors can be cooled by conduction, requiring no airflow inside themotor for cooling. This in turn means that the motor's internals can beentirely enclosed and protected from dirt or other foreign matter.

Brushless motor commutation can be implemented in software using amicrocontroller (e.g., controller 62) or microprocessor computer, or mayalternatively be implemented in analogue hardware, or in digitalfirmware using an FPGA. Commutation with electronics instead of brushesallows for greater flexibility and capabilities not available withbrushed DC motors, including speed limiting, micro stepped operation forslow and/or fine motion control, and a holding torque when stationary.

When converting electricity into mechanical power, brushless motors aremore efficient than brushed motors. This improvement is largely due tothe brushless motor's velocity being determined by the frequency atwhich the electricity is switched, not the voltage. Additional gains aredue to the absence of brushes, which reduces mechanical energy loss dueto friction. The enhanced efficiency is greatest in the no-load andlow-load region of the motor's performance curve. Advantageously, theuse of a brushless DC motor in refrigeration systems 50, 80, and/or 100may facilitate maintenance-free operation, high speeds, and operationwhere sparking is hazardous (i.e. explosive environments) or couldaffect electronically sensitive equipment.

Controller 62 may direct the rotor rotation of the brushless DC motorand may be configured to detect the rotor's orientation/position(relative to the stator coils). For example, controller 62 may use Halleffect sensors or a rotary encoder to directly measure the rotor'sposition. In other embodiments, controller 62 may measure the back EMFin the undriven coils to infer the rotor position, eliminating the needfor separate Hall effect sensors. Controller 62 may provide thebrushless DC motor with bi-directional outputs (i.e. frequencycontrolled three phase output), which are determined by controller 62.In various embodiments, controller 62 may use comparators to determinewhen the output phase should be advanced or use a microcontroller tomanage acceleration, control speed, and fine-tune efficiency.

In some embodiments, the brushless DC motor may constructed using aninrunner configuration or an outrunner configuration. In the inrunnerconfiguration, the permanent magnets are part of the rotor and threestator windings surround the rotor. In the outrunner (or external-rotor)configuration, the radial-relationship between the coils and magnets isreversed; the stator coils form the center (core) of the motor, whilethe permanent magnets spin within an overhanging rotor which surroundsthe core. The outrunner configuration may include more poles than theinrunner configuration (e.g., set up in triplets to maintain the threegroups of windings) and may have a higher torque at low RPMs. In someembodiments, the brushless DC motor may be constructed using stator androtor plates mounted face to face (e.g., for embodiments in which thespace or shape of the motor is limited).

In some embodiments, the brushless DC motor uses a delta configurationfor the electrical windings. The delta configuration connects threewindings to each other (series circuits) in a triangle-like circuit, andpower is applied at each of the connections. In other embodiments, thebrushless DC motor uses a Wye (Y-shaped) configuration or star winding.The Wye configuration connects all of the windings to a central point(parallel circuits) and power is applied to the remaining end of eachwinding. A motor with windings in the delta configuration gives lowtorque at low speed, but can give higher top speed. The Wyeconfiguration gives high torque at low speed, but a lower top speed.Controller 62 may treat both styles of windings in the same manner whenproviding control signals to the brushless DC motor.

It is contemplated that a brushless DC motor may provide advantages torefrigeration systems 50, 80, and 100 over conventional AC motors. Forexample, the brushless DC motor may significantly reduce the powerrequired to operate compressors 60 relative to a typical AC motor. Fans30, 64, and 88 can also be operated using a brushless DC motor in orderto increase overall system efficiency. In addition to the brushlessmotor's higher efficiency, refrigeration systems 50, 80, and 100 cantake advantage of a brushless DC motor's variable-speed and/or loadmodulation to adaptively operate compressors 60 to accommodate varyingrefrigeration loads. The use of controller 62 to control the brushlessDC motor allows for programmability, better control over fluid flow(e.g., refrigerant flow, airflow, etc.), and serial communication.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions and arrangement of the exemplaryembodiments without departing from the scope of the present disclosure.

The present disclosure contemplates methods, systems and programproducts on any machine-readable media for accomplishing variousoperations. The embodiments of the present disclosure may be implementedusing existing computer processors, or by a special purpose computerprocessor for an appropriate system, incorporated for this or anotherpurpose, or by a hardwired system. Embodiments within the scope of thepresent disclosure include program products comprising machine-readablemedia for carrying or having machine-executable instructions or datastructures stored thereon. Such machine-readable media can be anyavailable media that can be accessed by a general purpose or specialpurpose computer or other machine with a processor. By way of example,such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROMor other optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to carry or storedesired program code in the form of machine-executable instructions ordata structures and which can be accessed by a general purpose orspecial purpose computer or other machine with a processor. Wheninformation is transferred or provided over a network or anothercommunications connection (either hardwired, wireless, or a combinationof hardwired or wireless) to a machine, the machine properly views theconnection as a machine-readable medium. Thus, any such connection isproperly termed a machine-readable medium. Combinations of the above arealso included within the scope of machine-readable media.Machine-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing machines to perform a certain function orgroup of functions.

Although the figures show a specific order of method steps, the order ofthe steps may differ from what is depicted. Also two or more steps maybe performed concurrently or with partial concurrence. Such variationwill depend on the software and hardware systems chosen and on designerchoice. All such variations are within the scope of the disclosure.Likewise, software implementations could be accomplished with standardprogramming techniques with rule based logic and other logic toaccomplish the various connection steps, processing steps, comparisonsteps and decision steps.

Numerous specific details are described to provide a thoroughunderstanding of the disclosure. However, in certain instances,well-known or conventional details are not described in order to avoidobscuring the description. References to “some embodiments,” “oneembodiment,” “an exemplary embodiment,” and/or “various embodiments” inthe present disclosure can be, but not necessarily are, references tothe same embodiment and such references mean at least one of theembodiments.

Alternative language and synonyms may be used for anyone or more of theterms discussed herein. No special significance should be placed uponwhether or not a term is elaborated or discussed herein. Synonyms forcertain terms are provided. A recital of one or more synonyms does notexclude the use of other synonyms. The use of examples anywhere in thisspecification including examples of any terms discussed herein isillustrative only, and is not intended to further limit the scope andmeaning of the disclosure or of any exemplified term. Likewise, thedisclosure is not limited to various embodiments given in thisspecification.

The elements and assemblies may be constructed from any of a widevariety of materials that provide sufficient strength or durability, inany of a wide variety of colors, textures, and combinations. Further,elements shown as integrally formed may be constructed of multiple partsor elements.

As used herein, the word “exemplary” is used to mean serving as anexample, instance or illustration. Any implementation or designdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other implementations or designs. Rather,use of the word exemplary is intended to present concepts in a concretemanner. Accordingly, all such modifications are intended to be includedwithin the scope of the present disclosure. Other substitutions,modifications, changes, and omissions may be made in the design,operating conditions, and arrangement of the preferred and otherexemplary implementations without departing from the scope of theappended claims.

As used herein, the terms “approximately,” “about,” “substantially,” andsimilar terms are intended to have a broad meaning in harmony with thecommon and accepted usage by those of ordinary skill in the art to whichthe subject matter of this disclosure pertains. It should be understoodby those of skill in the art who review this disclosure that these termsare intended to allow a description of certain features described andclaimed without restricting the scope of these features to the precisenumerical ranges provided. Accordingly, these terms should beinterpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

As used herein, the term “coupled” means the joining of two membersdirectly or indirectly to one another. Such joining may be stationary innature or moveable in nature and/or such joining may allow for the flowof fluids, electricity, electrical signals, or other types of signals orcommunication between the two members. Such joining may be achieved withthe two members or the two members and any additional intermediatemembers being integrally formed as a single unitary body with oneanother or with the two members or the two members and any additionalintermediate members being attached to one another. Such joining may bepermanent in nature or alternatively may be removable or releasable innature.

The background section is intended to provide a background or context tothe invention recited in the claims. The description in the backgroundsection may include concepts that could be pursued, but are notnecessarily ones that have been previously conceived or pursued.Therefore, unless otherwise indicated herein, what is described in thebackground section is not prior art to the description and claims and isnot admitted to be prior art by inclusion in the background section.

What is claimed is:
 1. A refrigeration system for atemperature-controlled storage device, comprising: a refrigerationcircuit including a compressor driven by a brushless DC motor operableat multiple different speeds, a first heat exchanger, an expansiondevice, and a cooling unit in fluid communication via a first workingfluid; a cooling circuit including a pump and a second heat exchanger influid communication with the first heat exchanger via a second workingfluid such that the first heat exchanger is liquid-cooled by the secondworking fluid, the cooling circuit further including a valve operable tomodulate a flow rate of the second working fluid through the first heatexchanger; and a controller configured to operate the brushless DC motorat multiple different speeds to accommodate multiple different thermalloads experienced by the refrigeration system, each of the speedscorresponding to a different thermal load, wherein the controller isconfigured to modulate a speed of the brushless DC motor to maintain adesired temperature of a temperature-controlled space within thetemperature-controlled storage device, and the controller is configuredto operate the valve to maintain the measured pressure of the firstworking fluid at the inlet of the first heat exchanger at a desiredpressure.
 2. The refrigeration system of claim 1, wherein therefrigeration circuit further includes a first fan configured to providean airflow across the cooling unit to cool the airflow; wherein thecooled airflow is provided to the temperature-controlled space withinthe temperature-controlled device.
 3. The refrigeration system of claim2, wherein the controller is configured to modulate a speed of the firstfan to modulate a rate of heat transfer experienced by thetemperature-controlled space to maintain the desired temperature of thetemperature-controlled space.
 4. The refrigeration system of claim 2,wherein the controller is configured to operate the expansion device tocontrol a flow rate of the first working fluid passing therethrough andentering the cooling unit to modulate a rate of heat transferexperienced by the airflow flowing across the cooling unit to maintainthe desired temperature of the temperature-controlled space.
 5. Therefrigeration system of claim 2, wherein the controller is configured tomodulate the speed of the brushless DC motor to control a flow rate ofthe first working fluid circulating through the refrigeration circuit tomodulate a rate of heat transfer experienced by the airflow flowingacross the cooling unit to maintain the desired temperature of thetemperature-controlled space.
 6. The refrigeration system of claim 1,wherein the refrigeration circuit further includes a pressure sensorlocated at an inlet of the first heat exchanger and configured tomeasure a pressure of the first working fluid at the inlet of the firstheat exchanger.
 7. A refrigeration circuit for a temperature-controlledstorage device, comprising: a compressor configured to circulate a firstworking fluid through the refrigeration circuit; a variable-speedbrushless DC motor operable to drive the compressor; a heat exchangerconfigured to receive the first working fluid from the compressor andprovide cooling for the first working fluid; a valve operable tomodulate a flow rate of a second working fluid through the heatexchanger; an expansion device configured to receive the cooled firstworking fluid from the heat exchanger and expand the first working fluidto a lower-temperature state; a cooling element configured to receivethe expanded first working fluid from the expansion device and providethe first working fluid to the compressor; and a controller configuredto operate the variable-speed brushless DC motor at multiple differentspeeds to accommodate multiple different thermal loads, each of thespeeds corresponding to a different thermal load, wherein the controlleris configured to modulate a speed of the brushless DC motor to maintaina desired temperature of a temperature-controlled space within thetemperature-controlled storage device, and the controller is configuredto operate the valve to maintain the measured pressure of the firstworking fluid at the inlet of the first heat exchanger at a desiredpressure; wherein the compressor, the heat exchanger, the expansiondevice, and the cooling element are in fluid communication via the firstworking fluid.
 8. The refrigeration circuit of claim 7, furthercomprising a fan configured to provide an airflow across the coolingelement to cool the airflow; wherein the cooled airflow is provided tothe temperature-controlled space within the temperature-controlleddevice.
 9. The refrigeration circuit of claim 8, wherein the controlleris configured to modulate a speed of the fan to modulate a rate of heattransfer experienced by the temperature-controlled space to maintain thedesired temperature of the temperature-controlled space.
 10. Therefrigeration circuit of claim 7, wherein the controller is configuredto operate the expansion device to control a flow rate of the firstworking fluid passing therethrough and entering the cooling element tomodulate a rate of heat transfer experienced by an airflow flowingacross the cooling element to maintain the desired temperature of thetemperature-controlled space.
 11. The refrigeration circuit of claim 7,wherein the controller is configured to modulate the speed of thevariable speed brushless DC motor to control a flow rate of the firstworking fluid circulating through the refrigeration circuit to modulatea rate of heat transfer experienced by an airflow flowing across thecooling element to maintain the desired temperature of thetemperature-controlled space.
 12. The refrigeration circuit of claim 7,further comprising a fan configured to provide an airflow across theheat exchanger to cool the first working fluid flowing therethrough suchthat the heat exchanger is air-cooled.
 13. The refrigeration circuit ofclaim 12, further comprising a pressure sensor located at an inlet ofthe heat exchanger and configured to measure a pressure of the firstworking fluid at the inlet of the heat exchanger; and wherein thecontroller is configured to modulate a speed of the fan to control themeasured pressure of the first working fluid at the inlet of the heatexchanger.
 14. The refrigeration circuit of claim 7, wherein the heatexchanger is configured to be liquid-cooled with the second workingfluid.
 15. A refrigeration circuit for a temperature-controlled storagedevice, comprising: a brushless DC motor operable at multiple differentspeeds, the brushless DC motor driving a compressor that circulates afirst working fluid through the refrigeration circuit; a heat exchangerconfigured to provide cooling for the first working fluid; a valveoperable to modulate a flow rate of a second working fluid through theheat exchanger; and a controller configured to operate the brushless DCmotor at multiple different speeds to accommodate multiple differentthermal loads, each of the speeds corresponding to a different thermalload, wherein the controller is configured to modulate a speed of thebrushless DC motor to maintain a desired temperature of atemperature-controlled space within the temperature-controlled storagedevice, and the controller is configured to operate the valve tomaintain the measured pressure of the first working fluid at the inletof the heat exchanger at a desired pressure.
 16. The refrigerationcircuit of claim 15, further comprising: a cooling unit configured toprovide cooling for the temperature-controlled space by transferringheat from the temperature-controlled space to the first working fluid;and a fan configured to provide an airflow across the cooling unit tocool the airflow; wherein the cooled airflow is provided to thetemperature-controlled space within the temperature-controlled storagedevice.
 17. The refrigeration circuit of claim 15, wherein thecontroller is configured to modulate a speed of the fan to modulate arate of heat transfer experienced by the temperature-controlled space tomaintain the desired temperature of the temperature-controlled space.18. The refrigeration circuit of claim 15, wherein the controller isconfigured to modulate the speed of the brushless DC motor to control aflow rate of the first working fluid circulating through therefrigeration circuit.
 19. The refrigeration circuit of claim 15,further comprising: a fan configured to provide an airflow across theheat exchanger to cool the first working fluid flowing therethrough suchthat the heat exchanger is air-cooled; a pressure sensor configured tomeasure a pressure of the first working fluid at an inlet of the heatexchanger; and wherein the controller is configured to modulate a speedof the fan to control the pressure of the working fluid at the inlet ofthe heat exchanger.